Conventionally, the reinforcement of an automotive back door opener handle attaching portion is provided, for example, by such a structure as shown in FIGS. 7 and 8. Specifically, bent portions 32a and 33a of a pair of crank-shaped reinforcement members 32 and 33 are fitted to a door inner panel 31 constituting the inside surface of a back door 30 by spot welds S.sub.1 as shown in FIG. 8, and a pair of attaching portions 35 and 36 of a door outer panel 34, which are bent in an L shape toward the door inner panel 31, are put on bent portions 32b and 33b on the other side of the paired reinforcement members 32 and 33, by which these elements are fastened by bolting together with a handle case 37. In this case, the spot welds S.sub.1 of the reinforcement members 32 and 33 to the door inner panel 31 are made on the base plane of the door inner panel 31 (door inner panel base plane), and the fastening of the door outer panel 34 to the reinforcement members 32 and 33 is done on a plane, substantially parallel to the base plane of the door inner panel 31, at a distance .alpha. apart from the base plane of the door inner panel 31.
In FIG. 7, reference numeral 38 denotes a work opening formed in the door inner panel 31 to perform the work for connecting a back door opener handle 39 to an interlocking mechanism 40 (see FIG. 10), and 41 denotes a handle operating opening formed in the door outer panel 34 to operate the back door opener handle 39. The work opening 38 is a service hole having an opening area necessary for a box spanner 43 to be inserted, as shown in FIG. 10, during the work for connecting the back door opener handle 39 to an upper end 42a of an operating rod 42 (see FIG. 10) operated in connection with the turning operation of the back door opener handle 39 and when the door outer panel 34 is bolted to the reinforcement members 32 and 33 together with the handle case 37. In FIG. 8, reference numeral 44 denotes a door inner trim attached to the cabin-side surface of the door inner panel 31.
A latch reinforcing reinforcement member 50 as shown in FIG. 9 is sometimes used as another conventional reinforcement structure. In this case, the upper part of the latch reinforcing reinforcement member 50 is extended upward to provide a pair of attaching portions 51 and 52, and the attaching portions 35 and 36 of the door outer panel 34 (see FIG. 7) are bolted to the attaching portions 51 and 52 of the reinforcement member 50 assembled to the door inner panel 31.
However, the above-described conventional door structure has the following problems in either case. First, if variations exist in a distance .beta. between the door inner panel 31 and the door outer panel 34 at the back door opener handle attaching portion, that is, in a distance .beta. (see FIG. 8) between a door opener handle tightening plane of the door outer panel 34 and the door inner panel 31, in assembling the reinforcement member 32, 33 or 50 which has been assembled in advance to the door inner panel 31 to the door outer panel 34, the bolts are tightened in a state in which these elements interfere with each other or a gap exists between these elements. Therefore, there is a possibility of deformation, which mars the appearance, occurring at the corner of the door outer panel 34, that is, at a place indicated by arrow M in FIG. 8.
Also, the turning operation force for the back door opener handle 39 disposed to the door outer panel 34 acts in the direction such that the spot weld S.sub.1 portions which connect the reinforcement members 32 and 33 to the door inner panel 31 are separated, so that this construction is disadvantageous in terms of connection strength.
Further, because the back door opener handle 39 is connected to the upper end 42a of the operating rod 42 constituting the interlocking mechanism 40 of the back door opener handle 39 on the door inner panel 31, and because only the work opening 38 with a small opening area, which is necessary for assembling parts, is formed, if an excessive external force (impact force) is applied to the door outer panel 34 of the back door 30 from the rear side as indicated by arrows F in FIG. 10, the upper end 42a, a connecting portion 60 connecting with the back door opener handle 39, and the like of the operating rod 42 interfere with the door inner panel 31 due to the deformation of the door outer panel 34, so that there is a possibility that the back door is opened unexpectedly.
Also, because the distance .alpha. from the base plane of the door inner panel 31 to the attachment plane of the door outer panel 34 (the fastening plane between the reinforcement member 32, 33 or 50 and the door outer panel 34) is long as shown in FIG. 8, the accuracy of the reinforcement member attaching plane of the door inner panel 31 easily affects the attaching position of the reinforcement member 32, 33 or 50, so that the position of the handle operating opening 41 with respect to the back door opener handle 39 is not stabilized. Further, the door inner panel 31 has low strength. Also, the reinforcement member 32, 33 or 50 itself is large in shape because the distance .alpha. is long, so that this structure is disadvantageous in terms of cost and weight.